So what to make of 'Batman v Superman's' box-office plummet?

Few box-office indicators are more confounding than the second-weekend drop.

On the one hand, the drop -- the percentage of box-office dollars by which a release falls in its second weekend -- connotes that a film is neither good enough, nor has a fan base deep enough, to sustain itself beyond a strong opening.

On the other hand, to have ‎a big second-weekend drop you sort of need a big opening in the first place. So it can't be all bad.

Sound rough? It is. That percentage represents the eighth-largest drop in history for comparable films (those that took in at least $50 million in their opening weekends). It's a greater drop, by more than five percentage points, than "Transformers: Age of Extinction" and "Spider-Man 3." And those movies cratered.

Audiences stay away from a film in its second weekend for all sorts of reasons. But broadly speaking, big drops come in two categories. The first is for a movie that featured such pent-up demand--offered so many reasons for people to run out and see it--that it pretty much spent all its currency on opening weekend. Many of the people who were realistically going to see it came to the theater right when it came out.

They could do this thanks to a number of factors: because it's a hotly anticipated sequel, because it has some exceedingly strong pre-release awareness due to its brand, because the opening is such an event no one wants to be left out. That pretty much is what happened with "Harry Potter and the Deathly Hallows: Part 2," which combined all three.

In the summer of 2011, the anticipation was so great for the final film in the Potter series -- fans had in a sense spent a decade waiting for that moment -- that it drew a whopping $169 million its first weekend. Then there were few people left to see it, and it took in just $47 million its second weekend, a dip of 72%. (This also happened to "Fifty Shades of Grey" and, to a lesser extent, with several movies in the "Twilight Saga" series.) So many people were champing to see the film that the first weekend's numbers were massive--and the second weekend's inevitably much smaller.

The second category is when filmgoers hear about the movie from first-weekend early-adopters and decide it's not worth seeing. Example par excellence of this: "X-Men: The Last Stand," which after garnering $102 million on its opening weekend in May 2006 took a dive of nearly 67%, to $34 million, the following weekend. This was not an instance of a major "Harry Potter"-like event movie that had little new territory to mine. It's a case of a potentially solid-sized second-weekend audience shriveling up because of lackluster word-of-mouth.

The question, then, is which category "Batman v Superman" falls into. On the one hand, the film's opening was an event -- the meeting of major characters on the screen for the first time, the months of buzzy speculation, the chance to see actors such as Ben Affleck and Jesse Eisenberg as iconic superheroes/supervillains.

On the other hand, the word of mouth was, in fact, also weak. Really weak. Critics disdained the film -- a 29% score on Rotten Tomatoes -- and fans gave it a 'B' CinemaScore. Lest a B sound decent, like a B in AP chemistry, it isn't. Superhero movies, even bad ones, frequently tend to go in the A/A- range. When you get a B from hardcore fans who turned out to see it the first weekend, you're not in good shape. Two of the previous superhero films to garner B's were "Green Lantern" and "Catwoman." You see the problem.

So which camp is "BvS" in? One reason to think it's in the latter category -- that of the poor word-of-mouth socking it to a new film -- is that typically some of the biggest drops tend to happen in the summer moviegoing season, when a major new release comes along the following week to bump it off. Even "Deathly Hallows 2" faced competition the following weekend, from "Captain America: The First Avenger." But that doesn't tend to happen in this early-spring period, and it didn't happen to "BvS," which faced no legitimate new competition this past weekend.

Put another way, some wide-release summer movies are understandably going to get knocked down the next weekend because of all the competition moving in. (See under: "The Dark Knight Rises," which suffered a drop of more than 60%). Even "Man of Steel," Snyder's previous Superman entry, could chalk up some of its second-weekend drop to this factor. The film is being cited as a defense of sorts for "BvS" -- "Superman" fans all come out opening weekend, the argument's goes, as evidenced by "Man of Steel's" drop of more than 64%. But "Man of Steel" had to deal with the openings of "World War Z" and "Monsters University" in its second weekend. "BvS" had to deal with nothing much at all.

Studio accountants will not shed too many tears over the numbers for "BvS." The film currently stands at more than $260 million domestic and has taken in an additional $420 million overseas. But if "BvS" indeed endured a drop this weekend because audiences were turned off, it raises some red flags for future Warner Bros./DC Comics installments. The studio has bet big on the DC shared universe, with "Suicide Squad," "Wonder Woman" and "Justice League" all set to roll out in the coming years. If audiences are tired, or less enamored, it could be hard to bring them back.

One troubling precedent is the "X-Men" universe, which saw a drop-off in box office for several movies after "Last Stand" and was revived only earlier this year by "Deadpool."

Big drops have become more common in wide-release Hollywood. As marketing has taken on an ever-greater importance, box office tend to become frontloaded. But when less than one-third the number of people turn out on just the second weekend, it's troubling even by these new standards.

The counterexample to the big opening/wide drop is "My Big Fat Greek Wedding." Back in 2002, the film was the epitome of the slow-burn hit. Even when it expanded to more than 1,000 screens, it was suffering just small drops from weekend to weekend -- and, in some weekends, actually went up.

It seems fitting that "Batman v Superman" has opened against "My Big Fat Greek Wedding 2." Though the Nia Vardalos comedy sequel is hardly showing the kind of sustained momentum of its predecessor -- and its numbers are of course proportionally much smaller than the big-budget "BvS" -- the film is certainly holding its own. Thanks to some solid word-of-mouth, it dropped just 38% from its first weekend. A movie such as "Batman v Superman" lost much of its audience a week after it was released. But it doesn't have to be that way -- not when a lot of people like your movie, anyway.